Funding for this research was provided by:
Zoo of Barcelona (PRIC grant, 2016/2017)
Received: 7 May 2020
Accepted: 10 April 2021
First Online: 22 June 2021
: The Barcelona Zoo and the Leipzig Zoo controlled and approved all the procedures. Given that subjects participated on a completely voluntary basis, and no invasive procedures were used, no formal approval was required. During the tasks, moreover, individuals were never food deprived, and motivation to participate was ensured exclusively by the use of highly-preferred food (i.e. carrots). The experiments thus provided a form of enrichment for the subjects and did not present any risks or adverse effects on the animals.
: Not applicable.
: We declare we have no competing interests.